The role of the immune system in defending the brain against Alzheimer’s disease has been revealed in a study identifying 11 new genes that could help to trigger the most common form of senile dementia.
Key genes involved with the immune defences are among those newly identified as raising the risk of developing Alzheimer’s disease, which affects more than half of the 800,000 people in Britain with some form of dementia.
Scientists believe the findings support the belief that a failure of the immune system to clear out tangled proteins and other “debris” accumulating in the brain of Alzheimer’s patients may be central to how fast someone succumbs to the disease.
The same regions of the genome have also been found to play a role in multiple sclerosis and Parkinson’s disease, indicating that there may be common genetic factors behind the diseases, said Gerard Schellenberg of the University of Pennsylvania.
“We know that healthy cells are very good at clearing out debris, thanks in part to the immune response system,” Professor Schellenberg said.
“But in these neurodegenerative diseases where the brain has an inflammatory response to bad proteins and starts forming plaques and tangle clumps, perhaps the immune response can get out of hand and do damage,” he said.
The 11 genetic factors linked to Alzheimer’s doubles the number of genes known to play a role in the disease. Scientists hope to use the information to develop new drugs and to identify those people at greatest risk of developing the brain disorder.
Alzheimer’s disease is affecting an increasing number of people as the population ages. One in three people over 65 today will die with dementia – more than half with Alzheimer’s – but the number of patients with dementia will more than double to 1.7 millions by mid-century.
The international study, published in Nature Genetics, collected genetic sequences from nearly 75,000 people in 15 countries in order to tease out the genetic factors that appear to raise the risk of developing Alzheimer’s.
“A lot of work remains to clarify these new pathways and create new drugs,” said Philippe Amouyel of the Pasteur Institute in Lille, one of the leaders of the International Genomic Alzheimer’s Project.
“However, there is clearly a strong willingness in the scientific world to put together all our research capacities to move forward in the fight of this rapidly growing disease,” he added.
Concern over how governments in the developed world will cope with the growing number of people with Alzheimer’s has led to a special summit on dementia research in London in December, as part of the UK’s G8 presidency.
The international effort to find the scientific basis of the disease will be crucial for developing new treatments, said James Pickett, head of research at the Alzheimer’s Society.
“This truly global effort has doubled the number of genes linked to Alzheimer’s and showed what can be achieved when researchers collaborate,” Dr Pickett said.